As used herein an optical instrument is defined as any type of complex optical device including but not limited to telescopes, microscopes or similar optical devices. Typically, an optical instrument will include multiple optical elements such as mirrors, lenses, or prisms arranged to collect and focus light for observation, analysis or imaging. For example, a telescope may include an objective lens set, an objective mirror, or a combination of objective lens and mirror elements which function primarily to collect and focus light. Similarly, a microscope may include multiple selectable objective lens elements.
Both telescopes and microscopes configured for visual use also include ocular elements, commonly referred to as eyepieces, which are positioned in the optical system at or near the image plane formed by the objective. Alternatively, a camera having a film surface or electronic detector may be placed in the optical system at or near the image plane. In other instances an instrument such as a spectrometer may be positioned at or near the system focal plane. Typically, an optical system is designed so that eyepieces, cameras, imagers or other tools which in use are positioned at or near the image plane may be removed or interchanged as needed. For example, a telescope may be designed to interchangeably receive and hold various eyepieces having different selected focal lengths so that a user of the telescope may readily select an appropriate magnification and field of view for viewing an optical image. Similarly, optical instruments such as telescopes are typically configured to selectively receive either an eyepiece or an imaging device depending upon whether the user wants to record an image or directly view through the instrument. Furthermore, many important tasks such as the collimation of the optical elements in a complex optical instrument may be best performed with various tools which are received and held in the optical instrument at or near the eyepiece/image plane position.
Accordingly, telescopes, microscopes and similar optical instruments typically include an opening and clamping mechanism away from the objective, which opening is appropriately sized to receive and support the types of accessories which will typically be used with the selected optical instrument. For example, many telescopes and microscopes have an opening and associated clamping mechanism associated with a focusing mechanism that can receive selected eyepieces, the nose pieces of cameras, collimation tools or similar accessories. All of these accessories typically have a cylindrical barrel which is clamped into a corresponding cylindrical opening with a set screw or similar device.
The proper operation of an optical instrument requires that the various optical elements of the system be properly aligned with respect to an optical axis. For example, the proper operation of a telescope requires that the optical axis of the various lens elements within an eyepiece be aligned with the overall optical axis of the objective. Misalignment between these axes will introduce aberrations into the image viewed through the eyepiece. Similarly, the film plane or plane of an electronic image detector associated with a camera attached to a telescope must be normal to the optical axis of the telescope objective to avoid aberrations in the recorded image. Accordingly, it is desirable that an eyepiece holder support an eyepiece or other accessory such that the optical axis of the eyepiece or other accessory is both parallel to the main optical axis of the instrument and concentric with the main optical axis of the instrument.
As mentioned above, an eyepiece or accessory holder is typically sized to receive eyepieces or accessories having a standard barrel diameter. For example, most modern telescope eyepieces have a diameter of either 1¼ inches or 2 inches. Accordingly, the nose pieces for cameras or the barrels of other accessories such as collimation devices are also prepared to have either a 1¼ inch or 2 inch diameter. Many telescopes have an eyepiece holder which is slightly greater than 2 inches in diameter. By optionally using an adapter with a 2 inch outer diameter and a 1¼ inch opening, the 2 inch holder of the instrument may be utilized with both 1¼ or 2 inch diameter accessories and eyepieces.
Most known holders or adapters feature a slightly over-sized cylindrical opening into which the cylindrical barrel of an eyepiece or accessory is placed. The eyepiece may then be clamped with a set screw, multiple set screws, a collet or a combination of set screws and compression bands. The foregoing clamping strategies typically rely in part upon contact between the cylindrical exterior surface of the accessory and a cylindrical interior surface of the holder, a telescope drawtube for example. As shown in FIG. 1, a prior art holder 1 having a cylindrical drawtube 3 and a clamping mechanism such as set screw 5 allows significant misalignment between the accessory 7 and the primary optical axis. The source of much misalignment is the contact point 9 between the accessory barrel and the inner cylindrical surface of the drawtube 3. Misalignment can be reduced by precise machining of the corresponding surfaces; however this is not practical as very close tolerances will result in some accessories jamming in the drawtube opening. Also, the precision of the sizing of an accessory barrel is outside of the control of an instrument manufacturer.
There are two components to the potential misalignment. First, there may be lateral displacement of the axis of the accessory with respect to the primary optical axis. Lateral displacement does not destroy the parallel relationship between these two axes but does result in the primary and accessory axis no longer being concentric. In addition, the axis of the optical accessory may be tipped or skewed with respect to the primary optical axis, such that the parallel relationship of these axes is lost. In many applications moderate lateral misalignment can be tolerated, but even small amounts of tipping or skew will negatively affect optical performance. In other applications, such as imaging, or the precise collimation of instrument optics using collimation tools even relatively small levels of lateral misalignment or skew may be problematic.
The embodiments disclosed herein are directed to overcoming one or more of the problems detailed above.